Bonding, Structure and Properties of Matter

What are the three types of strong chemical bond?

Ionic, covalent + metallic.

When does ionic bonding occur?

Between metals + non-metals - electrons are transferred.

When does covalent bonding occur?

Between non-metal atoms - pairs of electrons are shared.

When does metallic bonding occur?

In metals + alloys - positive metal ions are attracted to delocalised electrons.

What happens to electrons during ionic bonding?

Electrons transfer from metal atoms to non-metal atoms.

How does a metal atom form a positive ion?

Loses one or more outer-shell electrons.

How does a non-metal atom form a negative ion?

Gains one or more electrons.

Why do ions form during ionic bonding?

Atoms gain or lose electrons to obtain a stable noble-gas electronic structure.

What charge do Group 1 ions form?

+1.

What charge do Group 2 ions form?

+2.

What charge do Group 6 ions form?

-2.

What charge do Group 7 ions form?

-1.

What does a dot-and-cross diagram show?

Outer-shell electrons + which atom the electrons originally came from.

What must be shown around ions in an ionic dot-and-cross diagram?

Square brackets + ion charge.

What is ionic bonding?

Strong electrostatic attraction between oppositely charged ions.

What structure do ionic compounds form?

Giant ionic lattice.

What is a giant ionic lattice?

Regular repeating structure of oppositely charged ions.

In what directions do electrostatic attractions act in an ionic lattice?

In all directions.

How do you determine the formula of an ionic compound?

Combine ions in a ratio that gives an overall charge of zero.

What is the formula of magnesium chloride from Mg2+ and Cl-?

MgCl2 - two Cl- ions are needed to balance one Mg2+ ion.

What is the formula of aluminium oxide from Al3+ and O2-?

Al2O3 - total positive and negative charges must balance.

What is an empirical formula?

Simplest whole-number ratio of atoms/ions in a compound.

What is a limitation of a dot-and-cross diagram?

Shows electron arrangement but not accurate sizes, distances or 3D structure.

What is a limitation of a ball-and-stick model?

Atoms/bonds are not to scale + sticks do not represent real physical rods.

What is a covalent bond?

Shared pair of electrons between two atoms.

Why is a covalent bond strong?

Strong electrostatic attraction between shared electrons + nuclei of the bonded atoms.

What type of bonding is found in H2, Cl2, O2 and N2?

Covalent.

How many covalent bonds are in H2?

1.

How many covalent bonds are in Cl2?

1.

How many covalent bonds are in O2?

2 - double bond.

How many covalent bonds are in N2?

3 - triple bond.

How many covalent bonds does hydrogen form?

1.

How many covalent bonds does oxygen normally form?

2.

How many covalent bonds does nitrogen normally form?

3.

How many covalent bonds does carbon normally form?

4.

What is the formula of hydrogen chloride?

HCl.

What is the formula of water?

H2O.

What is the formula of ammonia?

NH3.

What is the formula of methane?

CH4.

What types of structure can covalently bonded substances form?

Small molecules, polymers or giant covalent structures.

What is a polymer?

Very large molecule made from repeating units joined by strong covalent bonds.

What is a giant covalent structure?

Huge network of atoms joined by strong covalent bonds.

Give examples of giant covalent structures.

Diamond, graphite + silicon dioxide.

What is metallic bonding?

Strong electrostatic attraction between positive metal ions + delocalised electrons.

What does delocalised mean?

Electrons are free to move throughout the whole metal structure.

What structure do metals form?

Giant regular structures of positive ions surrounded by delocalised electrons.

What are the three states of matter?

Solid, liquid + gas.

How are particles arranged in a solid?

Close together in fixed positions - vibrate around these positions.

How are particles arranged in a liquid?

Close together but able to move past each other.

How are particles arranged in a gas?

Far apart + moving rapidly in random directions.

What happens at the melting point?

Solid changes to liquid.

What happens at the boiling point?

Liquid changes to gas.

What happens at the freezing point?

Liquid changes to solid.

What happens during condensation?

Gas changes to liquid.

What determines a substance's melting and boiling points?

Strength of forces/bonds between its particles - stronger forces require more energy to overcome.

Do atoms themselves have the bulk properties of the material?

No - bulk properties result from the structure + interactions between many particles.

What are limitations of the simple particle model?

Particles shown as solid spheres - no forces shown between particles - particle sizes/distances are not accurately represented. (HT)

What does (s) mean in a chemical equation?

Solid.

What does (l) mean in a chemical equation?

Liquid.

What does (g) mean in a chemical equation?

Gas.

What does (aq) mean in a chemical equation?

Dissolved in water - aqueous solution.

Why do ionic compounds have high melting and boiling points?

Many strong electrostatic attractions between oppositely charged ions require lots of energy to overcome.

Do solid ionic compounds conduct electricity?

No - ions are held in fixed positions and cannot move.

Why do molten ionic compounds conduct electricity?

Ions are free to move + carry charge.

Why do ionic compounds conduct when dissolved in water?

Ions separate and are free to move + carry charge.

What are small molecular substances usually like at room temperature?

Gases or liquids with relatively low melting + boiling points.

Why do small molecular substances have low melting and boiling points?

Weak intermolecular forces require little energy to overcome.

Are covalent bonds broken when a simple molecular substance melts or boils?

No - weak intermolecular forces between molecules are overcome.

How does molecular size affect intermolecular forces?

Larger molecules - stronger intermolecular forces.

How does increasing molecular size generally affect melting and boiling points?

They increase because intermolecular forces become stronger.

Why do simple molecular substances not conduct electricity?

Molecules have no overall charge + there are no free charged particles.

Why are polymers usually solid at room temperature?

Large molecules have relatively strong intermolecular forces between polymer chains.

Why do giant covalent structures have very high melting points?

Many strong covalent bonds must be overcome - requires lots of energy.

Why do most metals have high melting and boiling points?

Strong metallic bonds between positive ions + delocalised electrons require lots of energy to overcome.

Why can pure metals be bent and shaped?

Layers of atoms can slide over each other.

What is an alloy?

Mixture of a metal with one or more other elements.

Why are alloys harder than pure metals?

Different-sized atoms distort the regular layers - making it harder for layers to slide over each other.

Why do metals conduct electricity?

Delocalised electrons are free to move through the structure + carry charge.

Why do metals conduct thermal energy well?

Delocalised electrons transfer energy rapidly through the structure.

What structure does diamond have?

Giant covalent structure of carbon atoms.

How many bonds does each carbon atom form in diamond?

4 strong covalent bonds.

Why is diamond very hard?

Each carbon forms 4 strong covalent bonds in a rigid giant structure.

Why does diamond have a very high melting point?

Many strong covalent bonds must be overcome - requires lots of energy.

Why does diamond not conduct electricity?

All outer electrons are used in covalent bonds - no delocalised electrons/free charged particles.

What structure does graphite have?

Giant covalent structure made of layers of hexagonal carbon rings.

How many covalent bonds does each carbon form in graphite?

3.

Why can graphite layers slide over each other?

No covalent bonds between layers - only weak forces between them.

Why is graphite soft/slippery?

Layers can slide over each other easily.

Why does graphite have a high melting point?

Strong covalent bonds within the layers require lots of energy to overcome.

Why does graphite conduct electricity?

Each carbon has one delocalised electron free to move + carry charge.

How is graphite similar to metals?

Both contain delocalised electrons that can conduct electricity.

What is graphene?

A single layer of graphite - one atom thick.

What structure does graphene have?

Single layer of carbon atoms bonded in hexagonal rings.

Why is graphene very strong?

Strong covalent bonds between carbon atoms.

Why does graphene conduct electricity?

It contains delocalised electrons that can move through the structure.

Why is graphene useful in electronics and composites?

It is strong, very thin + conducts electricity.

What are fullerenes?

Molecules of carbon with hollow shapes.

What rings are found in fullerenes?

Mainly hexagonal rings - may also contain rings of 5 or 7 carbon atoms.

What is Buckminsterfullerene?

C60 - spherical fullerene containing 60 carbon atoms.

What are carbon nanotubes?

Cylindrical fullerenes with very high length-to-diameter ratios.